Problem: $ \left(\dfrac{5}{4}\right)^{-4}$
Explanation: $= \left(\dfrac{4}{5}\right)^{4}$ $= \left(\dfrac{4}{5}\right)\cdot\left(\dfrac{4}{5}\right)\cdot \left(\dfrac{4}{5}\right)\cdot \left(\dfrac{4}{5}\right)$ $= \dfrac{16}{25}\cdot\left(\dfrac{4}{5}\right)\cdot \left(\dfrac{4}{5}\right)$ $= \dfrac{64}{125}\cdot\left(\dfrac{4}{5}\right)$ $= \dfrac{256}{625}$